These Old Shades by Georgette Heyer

And Paris began to talk, in whispers at first, then gradually louder, and more openly. Paris remembered an old, old scandal, and said that the English Duc had adopted a baseborn daughter of Saint-Vire in revenge for past injuries. Paris thought that it must irk Saint-Vire considerably to see his offspring in the hands of his greatest enemy. Then Paris wondered what the English Duc meant to do with Mademoiselle de Bonnard, and found no solution to the riddle. Paris shook its head, and thought that the ways of Avon were inscrutable and probably fiendish.

Meanwhile Lady Fanny swept through the town with Léonie, and saw to it that her social activities this season should not easily be forgotten. Léonie enjoyed herself very much, and Paris enjoyed her even more. In the mornings she rode out with Avon, and two factions sprang up thereafter amongst her admirers. One faction held that the divine Léonie was seen at her best in the saddle; the other faction was firm that in the ballroom she was incomparable. One excitable young gentleman challenged another on this score, but Hugh Davenant was present, and he took both young hotheads severely to task for bandying Léonie's name about over their cups, and the affair came to naught.